Hello! I just wanted to add something quickly. I've spilled some water on my macbook air mouse pad and wifi stopped working, it said "no hardware installed". I tried to do PRAM, nothing helped - I must've actually damaged the wifi card inside. I was considering getting a new macbook or getting it fixed (but then I was a bit worried it would take long and I could lose my data). In the end I found a perfect solution - I got a wifi dongle (extension) - you plug it in an usb port and it looks like a small pendrive. Now I can connect to the internet through it and I only spent £16 instead of £300 for fixing the thing. You can consider this solution!